The present invention relates to a method for controlling a supercharged engine, particularly an indirect injection engine, and an engine using such a method.
In general, the power delivered by an internal combustion engine is a function of the amount of air introduced into the combustion chamber of this engine, which quantity of air is itself proportional to the density of this air. As is known, this air can be compressed, by any compression means, such as a turbocompressor, before its admission into the engine cylinder in order to supercharge this cylinder with air.
In order to improve this filling with air still further, provision is made to evacuate the residual burned gases from the combustion chamber before the end of the exhaust phase of the engine, and replace them with supercharged air, a stage which is more commonly known as burned gas scavenging.
As is better described in U.S. Pat. No. 4,217,866, this scavenging is effected by having, at the end of the exhaust phase, an overlap phase between the exhaust and inlet valves of one cylinder. More specifically, this overlap is effected by simultaneously opening the exhaust and inlet valves, by several degrees to several tens of degrees of crankshaft rotation angle, near the top dead center (TDC). For this, a specific intake means is provided, comprised of a pipe and a valve, for supercharged non-fuel-containing air, in addition to a conventional intake means, also comprised of a pipe and a valve, provided to admit supercharged fuel-containing air into the combustion chamber. This burned gas scavenging is thus effected by overlapping the exhaust valve and the supercharged non-fuel-containing air valve. During this overlap, the exhaust valves remain open and supercharged non-fuel-containing air is admitted into the combustion chamber. This supercharged non-fuel-containing air, which is at a higher pressure than that of the burned gases, scavenges these gases and evacuates them through the exhaust valve or valves thus filling the space freed by these gases. At the end of scavenging, the exhaust valves close and supercharged fuel-containing air is introduced into the combustion chamber by another intake means which is provided with a fuel injector in the case of multipoint fuel injection.
This type of engine, although it gives satisfaction, nonetheless has several non-negligible drawbacks.
In certain operating modes of a multicylinder engine, especially at high speed and full load, a counter-scavenging phenomenon occurs in the cylinder and prevents the residual burned gases from evacuating. This counter-scavenging is generally due to the rising of a puff of exhaust gas from a cylinder at the start of the exhaust phase going to the cylinder which is in the terminal exhaust phase and in which the scavenging occurs. In this case, during scavenging, the supercharged non-fuel-containing air inlet valve is open and since the pressure of the exhaust gas puff is greater than the supercharged air pressure, the air inlet is blocked and residual exhaust gases pass into the non-fuel-containing air inlet pipe. These gases in the pipe are then readmitted into the combustion chamber in the intake phase of the engine.
This has the disadvantage of uncontrollably modifying the level of residual gases contained in the combustion chamber and impairing the combustion that occurs subsequently.
To remedy the foregoing, provision is made so that the means commanding the movement of the inlet valves, such as a camshaft, are such that the valve of the non-fuel-containing air intake means can remain constantly closed until the end of the engine exhaust phase to eliminate the overlap phase between the supercharged non-fuel-containing air valve and the exhaust valve. For this purpose, this camshaft has a phase shifter preventing the non-fuel-containing inlet valve from opening until the exhaust valves are closed.
Such a phase shifter has a complicated design, requires precise regulation, and increases the cost of the inlet valve control means.